In a gas turbine engine, operational efficiency generally increases as the temperature of the combustion stream increases. Higher combustion stream temperatures, however, may produce higher levels of nitrogen oxides (“NOx”) and other types of emissions. Such emissions may be subject to both federal and state regulation in the United States and also subject to similar regulations abroad. A balancing act thus exists between operating the gas turbine engine in an efficient temperature range while also ensuring that the output of NOx and other types of regulated emissions remain below the mandated levels.
Several types of known gas turbine engine designs, such as those using Dry Low NOx (“DLN”) combustors, generally premix the fuel flows and the air flows upstream of a reaction or a combustion zone so as to reduce NOx emissions via a number of premixing fuel nozzles. Such premixing tends to reduce overall combustion temperatures and, hence, NOx emissions and the like.
Premixing, however, may present several operational issues such as flame holding, flashback, auto-ignition, and the like. These issues may be a particular concern with the use of highly reactive fuels. For example, given an ignition source, a flame may be present in the head-end of a combustor upstream of the fuel nozzles with any significant fraction of hydrogen or other types of fuels. Any type of fuel rich pocket thus may sustain a flame and cause damage to the combustor.
Other premixing issues may be due to irregularities in the fuel flows and the air flows. For example, there are several flow obstructions that may disrupt the flow through an incoming pathway between a flow sleeve and a liner. With a combustor having fuel injector vanes that inject fuel into the airflow upstream of the head-end, these flow disturbances may create flow recirculation zones on the trailing edge of the vanes. These recirculation zones may lead to stable pockets of ignitable fuel-air mixtures that can in turn lead to flame holding or other types of combustion events given an ignition source.
There is thus a desire for an improved combustor design. Such a design should accommodate flow disturbances upstream of the fuel injectors so as to avoid flame holding, flashback, auto-ignition, and the like. Moreover, an increase in the flame holding margin may allow the use of higher reactivity fuels for improved performance and emissions.